It’s one of America’s great recycling success stories: Every year, hundreds of thousands of discarded Christmas trees are collected and reused.

Many are picked up curbside by local garbage collection services and turned into mulch. But there are other second acts for Christmas trees, too. They’re placed on beaches to shore up dunes and sunk in lakes as fish habitats. They’ve even been milled into lumber for use in building homes.

How many of the 25 million to 30 million fresh Christmas trees sold each year are recycled is difficult to measure because most recycling programs “are implemented on such a local level,” says National Christmas Tree Association spokesman Rick Dungey. The good news, though, is that tree-recycling efforts are now “ubiquitous” and recycling your tree is “easier than ever.”

This will be the 27th year for Christmas tree recycling in San Francisco, where nearly 600 tons of trees are fed into a giant wood-chipper outside City Hall each year and turned to mulch. New York City’s Department of Sanitation collects about 150,000 trees each year and mulches them in a joint program with the Parks Department. The mulch is used in parks, playing fields and community gardens. Residents lucky enough to have their own urban backyards can take home a bag at “Mulchfest” events held around the city.

New York’s Rockefeller Center is famous for its towering Christmas tree, and for the seventh year in a row, this season’s tree will be donated to Habitat for Humanity. The tradition began when the 2007 Rockefeller Center tree went to build a home in Pascagoula, Miss., for a survivor of Hurricane Katrina.

Lumber from the milled Rock Center tree is marked so that the families know its origin. In some years, families that have benefited from the construction have attended the tree-lighting event in Manhattan.

In Jefferson Parish, a suburb of New Orleans, Christmas trees help prevent marshland erosion. The trees are placed in wooden cribs, in shallow water parallel to the shore, where they absorb the impact of waves.

“It protects the shoreline,” explains Jason Smith, spokesman for the Jefferson Parish Department of Environmental Affairs. “The area behind it is calm, where vegetation can grow.” The trees decompose and must be replaced yearly. The program uses between 10,000 and 30,000 trees a year, and has been in existence since the winter of 1990-91.

Shawnee Mission Park Lake in Shawnee, Kan., is also a final resting place for recycled Christmas trees. About 100 to 150 trees are sunk each year with concrete blocks to provide fish habitat.

Many beaches also use recycled Christmas trees to protect against erosion. Strategically placed, the trees catch sand and are eventually covered by it, becoming part of the dune system.

A number of beaches at the New Jersey shore were built up using Christmas trees after last year’s Superstorm Sandy. Beaches at the Rockaways, in New York City, which were also devastated by Sandy, benefited from a Christmas tree project as well. The Rockaways effort was sponsored by a California wine company, Barefoot Wine & Bubbly, an E. & J. Gallo Winery brand. Barefoot Wine has been working with the Surfrider Foundation, which promotes ocean protection, on beach cleanups and restorations for seven years. But the Rockaways program was Barefoot’s first using recycled trees.

Those who prefer artificial Christmas trees usually don’t throw them out after one year. But when the time comes, there’s even a program to recycle them. Polygroup, one of Walmart’s largest suppliers of artificial Christmas trees, sends them — including lights and electric cords— to a recycling center in China where they are shredded and broken down for reuse in other products. The bad news: Consumers must pack and ship the trees back to Polygroup themselves. The good news: You can send in any brand of tree, and you need only ship to Polygroup’s Indiana offices, not to China.